The present invention relates generally to the arming of fuzes used with artillery shells. More particularly, the present invention relates to a method of and apparatus for arming a mortar proximity fuze at the apex of the trajectory of the mortar shell.
At the present time, the M734 mortar proximity fuze arming is controlled by a setback sensor and the turbine alternator, both of which components form part of the mortar. At the time the mortar round is launched, the set-back sensor detects a valid launch condition and removes one lock from the safety system. Gears in the safety and arming device then count the turns of the turbine-alternator rotor and withdraw the second safety lock after approximately 1,000 turns. After the second safety lock has been withdrawn, the safety and arming device rotor moves into the "armed" position and the mortar round is then armed to explode at a predetermined height above its target.
In mortar rounds which utilize electronic arming, such systems are based on a simple analog timer. Approximately 2.5 seconds after the turbine-alternator starts providing power, the electronic arming circuits are "armed" and ready to fire the warhead at the predetermined height above the target.
The known methods and apparatus for arming mortar proximity fuzes function to arm the mortar fuze shortly after the round is launched. Once the fuze is armed, it is intended to explode without hurting the launch crew. However, since the fuze is a simple and low-cost Doppler fuze, it is vulnerable to system and environmental noise that can cause explosions of the round before it reaches its predetermined altitude. While production fuzes easily meet the design specifications of less than 1 percent above 30 feet over the target, premature explosions shortly after firing from the mortar tube have an adverse psychological impact on the troops using the mortar rounds.
In contrast to the known prior art methods and apparatus, the present invention utilizes a method of and system for avoiding the early explosion of the mortar round before it has reached the apex of its trajectory by not electrically arming the fuze until it is halfway through its expected flight time. The instant invention thus serves to decrease the chance of an early explosion of the round by 50 percent and therefore improves the perceived "goodness" of the fuze with a consequent beneficial psychological impact on the troops using the mortar round.